Modulation



June 3U, i793.

G. L. ussELMAN MODULATION 5 sheets-sheet 1 original Filed oct. 15, 1932 INVENTOR GEORGE L. USSELMAN WZ/M ATTORNEY l @me w, w3@ G. L. UssELMAN MODULATION 'original Filed oct. 15, 1932.

5 Sheets-Sheet 2 INVENTOR GEORGE L, USSELMAN BY ),QQ

ATTORNEY june 30, i936. G. L.. USSELMAN MODULATION Original Filed Oct. l5, 1932 5 Sheets-Sheet 3 INVENTOR GEORGE L. SSELMAN ATRNEY N A M L E s S U L G.

MODULAT ION Original FiledOot. l5, 1932 5 Sheets-Sheet 4 @l All INVENTOR GEORGE L. ZELL/MN ATTORNEY Hume 30,1936. G. 1 USSELMAN MODULATI'ON original Filed oct. 15, 1932 5' Sheets-Sheet 5 k IWI Tv, m.

, INVENTOR GEORGE BY Lg mIUSSELMAN WW ATTORN EY Patented June 30, 1936 UNITED STATES PATENT OFFICE MODULATION George Lindley Usselman, Port Jefferson, Long Island, N. Y., assigner to Radio Corporation of America, a corporation of Delaware Original application October 15, 1932, Serial No. 637,923.y Divided and this application May 2, 1934, Serial No. 723,425

13 Claims. (Cl. 179-171) This invention relates to signalling means and More in detail, this invention relates to an imin particular to means whereby the characteristics proved modulating means wherein a single phase of high frequency oscillations other than amplimodulator stage is preceded by an amplitude tude are varied in accordance with signals to be modulator stage which comprises a pair of tubes transmitted. This application is a division' of having control grids connected in circuits and 5 my United States application No. 637,923 led energized at carrier frequency in phase. In ac- October 15, 1932. v cordance with the present invention each tube is It has been found `that ordinary amplitude equipped with its own separate tank circuit.

modulated high frequency oscillations in trans- Moreover, in the present invention, instead of mission from the sending station to the receiving phase modulating the energy reaching the grids 10 station are subject to What is known as fading of these two tubes, the phase shifting means is effects. This is a decided disadvantage since it interposed between the separate tank circuits introduces drop-outs and errors in the signal. and the control electrode of the single tubefin Even where diversity receivers are used to rethe following stage. I-Iere, as in the'prior appli- 5 ceive the amplitude modulated signals the effect cations, the internal imDedemCeS of the pair of l5 of fading is of serious disadvantage. tubes are varied in opposite senses by the modu- I have found that if the high frequency oscillating frequencies. In the present Case thisrelations are modulated in phase or in frequency in sults in amplitude modulation of the Carrier. accordance with the signal to be transmitted This modulated energy iS then fed by Way of g() they are'somewhat less subject to the yeffect of phase Shifting elements t0 the Control grid 0f the 20 fading than amplitude modulated waves, assum- Single phase modulator tube- Y ring like amounts of power are utilized in the The noVel features' 0f my invention have been transmission. Phase or frequency modulation is pointed out With Pel'tioulerity in the Claims aD- advantageous because it allows the transmitter to pended hereto.

operate at full output power, whereas in ampli- The nature of my invention and the operation tude modulation it is necessary to reduce the thereof will be best understood from the folpower and operate the transmitter ai; about; one lowing detailed description thereof and therefrom fourth of the full transmitter power output. lThe When read in connection with the drawings. increased Signal Strength gained by phase or frethroughout which like reference numerals indi- 5-0 quency modulation is a great advantage for recate like parts, andin Which; V 30 ducing fading and for increasing the reliability Figure 1 illustrates e Speoio embodiment of of the service. the invention; while,

In each of my United States applications, Serial Figures 2, 3. 4, and 5 illustrate modifications of No. 623,558, led July 20, 1932, Serial No. 616,026, the arrangement of Figure 1.

filed June 8, 1932, Patent #2,036,165 dated March A specific embodiment of my invention is shown 31, 1936, serial No. 602,487, med April 1, 1932, in Figure 1. In this fleure A iS a Source of con- Serial No. 607,932, filed April 28, 1932, Patent stant frequency oscillations, such asacrystal con- #2,036,164 dated March 31, 1936, I have shown trolled oscillator or a long line frequency conmeans for varying at signal frequency the chartrolled oscillator. The oscillator A is connected acteristics other than the amplitude of a carrier in parallel by Way 0f blocking condensers I and 3 40 frequency. In each of these arrangements the to the control grids 2 and 4 of tubes G and H recarrier frequency is impressed through phase SpeCtiVely of Stage C- The tubes G and H are shifting means onto the control grids of a pair shown as the screen grid types although three eleof thermionic tubes which have their anodes conment tubes may be uSed- In the latter Gase neunected in parallel to a common tank circuit and traliZing CirGuitS` may be necessary The anode 45 their internal impedances varied in phase opelectrodes 6 and 8 of tubes G and H respectively position by the signal wave. In each of these arare connected to tank circuits M and N respecrangements the phase modulator stage comprises tively. Tank circuit M includes a variable capactwo tubes having their input electrodes symity l0 and an induotarloe l|- The tank Circuit N' metrically connected and energized as indicated includes a variable capacity I0 and inductance 50 above, and a common tank circuit connected in I I. The alternating current circuits for tubes G parallel to the anodes of said pair of tubes. and I-I are completed by connecting the lower ter- The'present invention relates to an improved minals of tank circuits M and N by Way of bymodulating means broadly of the type referred passing condensers C1 to the grounded side of the to above. circuit I2 supplying heating current from the 55 source K to the cathodes of the tubes. The energizing circuits for anodes 6 and 8 are completed by way of a lead I3 connecting the terminals of inductances II and II' to the source K. Tank circuitM is connected through a blocking condenser O to one end of the phase retarding element L. Tank circuit N is connected through a blocking condenser P to one endl of the phase advancing element Q. The other ends of both phase shifting elements are connected together as'- shown and to the grid S of tube I in stage D.

The alternating current input circuit of tube I is completed by way offradio frequency choking inductance I4 and by-pass condenser I5 connected between the grid S and cathode' I6 of tube I. The cathode I6 is maintained at stable potential by connecting one side thereof to ground G as shown. The desired negative potential may be supplied to the grid S by way of choke coil I4 and lead II connected with source I8. The alternating current anode'cathodecircuit of tube I comprisesY the anode 20, tank circuit R, by-pass condenser 2|, and the grounded side of cathode I6. Thedirect current anode cathode circuit of tube I comprises the anode 20, the inductance 22 of tank circuit R, a portion of the source I8,

andthe cathode lr6. Tank circuit R may be tuned to the desired frequency by a Variable capacity 23 connected in parallel with inductance 22. The tube I4 is of thek screen grid type and charging potential is supplied to the screen grid electrode 24 by;a lead 25 connected to a point on source I8. Any radio frequency potentials appearing on 24 -are shunted around source I8 by a by-pass condenser 26 It will be understood that the screen grid tubeI may be replaced by a three-electrode ltube provided proper precautions are taken to obtain stable operation thereof. It should be 'understood that sources K and I8 may be of any desirable type, such as, storagev batteries, motor generator sets, or vacuum tube rectifiers.

The tank circuit R of stage D is connected, by

'asshown by way of radio frequency inductances 32 and 32' to the control grids 2 and 4 of tubes G and H respectively, as shown. The inductances 32` and 3:2" may be replaced-by resistances` ifr desired. In order` that radio frequencies appearing` in inductances 32 and 32 do not reach the modulation frequency' transformer T1 and source B connected therewith, the lower endsof inductances 3.2` and4 32' are connected by wayl of bypassing condensers 33"and 33 to thev grounded lead of the cathode heating circuit I2. The proper biasing potentials are applied to the control electrodesy 2 and 4 by way of the secondary winding 3I and a 'lead 34I connecting the midpoint thereof to a potentiometerI P connected inA shunt with a portion of direct currentsource K.V Charging potentials for the screen grid electrodes136 and 36' of tubesG and H are supplied by way of lead 31" connected to a point on potentiometer vresistance P shuntedacross source K. Alternating current appearing onthe grid electrodes -36, 3G' is shunted around source K by lby-pass condensers 38 and- 38 connected as shown..

In operation the oscillator A supplies equal amounts of high frequency excitation voltage to each of the control grids 2 and 4 of tubes G and H in stage C. If there is no signal frequency being supplied to the control grids 2 and 4 from B by way of T1, this high frequency energy will l be arnplied equally and, if desired, multiplied in frequency in tubes G and H and tank circuits M and N respectively. This follows from the fact that like potentials are applied to the electrodes of these two tubes and also to the fact that tank circuits M and N are made to be of similar` characteristics. Furthermore (still assuming no potentials are supplied from B), since in practice the impedances of phase retarding element L and phase advancing element Q are of equal magnitude, the high frequency energy reaching the grid S of tube I in stage D,.from tank. circuit M and from tank circuit N, will be of equal intensity. The energies will have equal phase angles-that is, one leading'and the other lagging, about the average phase position. The resultant phase of the excitation energy supplied to S from M and N will in this case lie midway between the phase angles'of the separate energies supplied from M and N. Stage D amplifles, or, if it is desired, may be adjusted to multiply the carrier frequency before it istransmitted to stage E. As I have said before, the

carrier energy may be limited and multiplied'` in f frequency or amplified, or both, in stage E. From the last stage, the carrier energy is transmitted through the transmission line V -V to antenna F, where it is radiated into space.

If we now assume that signal frequency is trol grids 2 and- 4. Now take some instant` in the signal when the grid 2 of tube G will be swung, say, in a positive direction, while the grid 4 of tube H will be swung an equal amount in a negative direction.

The carrier energy produced in oscillator A is delivered in two equal parts to the grids .2 and 4 of tubes G and H respectively in stage C. One portion is amplified in amplifier G and appears in tank circuit M, while the other portion is amplified in amplifier H and appears in tank circuit N. This amplification is not constant Vbecausethe amplified energies in the two amplifiers G and H are differentially modulated in amplitude so that Vthe carrier energies delivered by the two amplifiers are of the same phase angle, but of an amplitude which varies at signal frequency and which is proportional to the signal intensity. Due to the actionof the modulating transformer T1 this variation in amplitude is made opposite for each amplifierV about an average Value. 'Ihis differential action will increase the power output of tube G- and tank circuit M, while the power output of tube H and tank circuit N will be decreased a like amount, or vice versa. The phase deviation or shift caused by L and Q in the two high frequency energiesA supplied tothe grid S of tube I will be equal but the energiesA will be of unlike sense, Vand in thisV case the power supplied from tank circuit M through phase retarding element L will be greater than ffl amplitude or average.

the power supplied from tank circuit N through phase advancing element Q.

The carrier energy from the tank circult M connected with amplifier G passes through the phase retarding element L, while the carrier energy delivered by the amplifier H to the tank circuit N passes through the phase advancing element Q. These two differentially modulated carrier energies are impressed on the grid electrode S of tube pedance of L and Q should be made equal so that they have equal effect on'the amplitude of the carrier energies delivered thereby from tank circuits M and N to controlgrid electrode S. It can Ibeseen that We now have two carrier energies of the same frequency present on the grid S of tube I and that these two carrier energies have a constant phase difference but are of an amplitude which varies differentially about a constant total In other words, the total energy delivered to the grid S of tube I is constant and the phase angle between the two parts of this energy is also constant. Each of these two parts of the total carrier energy is amplified or multiplied in frequency, or both, in tube I and delivered to the tank circuit R of the stage D. Tank circuit R has only one degree of freedom, that is, the carrier frequency or a desired harmonic of the carrier frequency to which the tank circuit may be tuned so that there can be but one oscillating current in the tank circuit R. Because of the phase difference of the two energies fed into the tank circuit the phase of .the oscillating current in the tank circuit will be determined or controlled to a greater extent or made to shift toward that of the carrier energy having the greater amplitude. The amount of the shift will be proportional to the excess energy of one part of the carrier energy over the other part of the carrier energy. The amount of shift in phase of the carrier energy is limited by the value of the reactances of the phase shifting elements L and Q, as has been explained before. This results in carrier energy in the tank circuit R of stage D, which will be of substantially constant amplitude but of varying phase angle. The frequency of the variation of this phase angle is the signal frequency and the degree or amount of phase swing or phase deviation is substantially proportional to the amplitude of the signal. The amo-unt of phase modulation is also controlled by the values of the phase shifting elements L and Q. If the energy in tank circuits M and N are linearly amplitude modulated in phase opposition, the phase of the energy appearing in tank circuit R of stage D will y be linearly phase modulated.

The energy delivered from stage D may be utilized in any desired manner. They energy may be amplified or multiplied in frequency and it may be radiated from the antenna F. When `the frequency of the phase modulated carrier is multiplied the angle of phase modulation is increased in the same ratio.

In some cases it maybe desirable to impress the modulating potentials on the internal impedances of tubes G and H in a different manner than that in which they are impressed on said impedances in Figure l. For example, it may be desirable to apply the signal oscillations from B by way of the secondary winding of transformer T1 to the screen grid electrodes 36, Sii' of tubes G and H respectively in phase opposition, as shown in Figure 2 of the drawings. When the modulating potentials are applied in phase opposition to the screen grid electrodes of tubes G and H steady positive charging potential for said electrodes is supplied by Way of a lead 31' connected to a point on the resistance of potentiometer P1 as shown. In this novel modulating scheme the desired negative bias is applied to the control electrodes 2 and #i of tubes G and H by way of a lead 34 connecting said electrodes to a point on the resistance of potentiometer P. 'I'he modulated transmitter of Figure 2 is otherwise the same as the transmitter .oi Figure l.

The operation of the arrangement of Figure 2 is similar' to the operation of the arrangement of Figure 1. The only diierence between the two arrangements is that in Figure 1 the impedances of the tubes G and H are varied in opposition at signal frequency by varying the effective potential on the control grid electrodes, whereas in the arrangement of Figure 2 the impedances of tubes G and H are varied in phase opposition atsignal frequency by varying the effective charging potential applied to the screen grid electrodes. In each case thn carrier frequency relayed in tubes G and H is differentially modulated in amplitude at signal frequency.

In yet other cases it may be desirable to accomplish the amplitude modulation of the carrier in the stage C by means of modulating the anode potentials. When this method of modulating is desired the arrangement of Figure 3 may be used. In Figure 3 the proper negative biasing potentials are supplied to the controlV grids of tubes G and H by a lead 3f as in Figure 2. Direct current potentials for the screen grid electrodes of tubes G and H are supplied by way of a lead 31, as in Figure .1.. In this arrangement, however, the modulating potentials from the source B are supplied by way of transformer T1 in phase opposition to the anodes 6 and 8 of tubes Gand H respectively. amplitude of the carrier waves passed by tubes G and H is accomplished in the stage C. In other Arespects the arrangement shown in Figure 3 operates the same as the arrangement of Figure 1.

A repetition of the operation of these novel modulating arrangements in connection with Figure 3 is thought unnecessary.

When plate modulation of the amplitude of the Vcarrier in the unit C by a more efcient method is desired, the arrangement of Figure 4 may be used. In this arrangement the tubes G and H are of the three-electrode type. Three-electrode tubes are used in this arrangement because, when the amplitude modulation of the carrier is accomplished by varying the anode potential, the three-electrode tubes give much greater response than that obtainable with the four-electrode tubes of Figure 3. When three-electrode tubes are used'the capacity between the anode electrodes and grid electrodes of the tubes G and H may be neutralized by plate circuit neutralization. This is accomplished by connecting the lower terminal of the tapped plate inductances il and Il tothe control electrodes 2 and 4 of the tubes G and H respectively by' way of variable neutralizing capacities NC and NC' respectively. The charging potential for the anode electrodes 6 and 8 is supplied from the lead I3 connected to the midpoint of the secondary Winding 3l of transformer T1 and by leads connecting the ends of the secondary winding 3| of transformer T1 to the points tapped to the inductances ll and l l. The arrangement of Figure 4 is otherwise similar to the arrangement of Figure 3,

The phase modulator of Figure 4 operates the In this manner anode modulation inA t same as the phase, modulator of Figure 1. The high frequency oscillations from A are impressed cophasally in equal amounts onto the control electrodes of G and H respectively. These oscillations may be amplified or frequency multiplied, or both, in the tubes G and H, and in particular in the output circuits thereof. The high frequency oscillations, whether amplified, frequency multiplied, or both, are differentially modulated in amplitude in stage C in accordance with the signal impressed from source B in phase opposition on the anode electrodes of tubes G and H. The carrier energies from M and N, which are of the same phase but of amplitude which varies at signal frequency, are fed through the phase shifting means L and Q to the control electrode S of tube I. The action of the phase shifted energies from M and N on the control electrode S of tube I results in the production in tank circuit R. of energy, the phase of which varies at signal frequency, but the amplitude of which is constant, as has been described in detail hereinbefore in connection with Figure l. The frequency of the phase modulation of this energy is directly proportional to the signal frequency and the degree of phase shift is proportional to the amplitude of the signal, except as otherwise modied by the phase shifting elements L and Q of ystage C. The energy from tank circuit R is fed by Way of coupling unit U to the unit E, from which it may be radiated. The unit E may include amplitude limiters or amplitude amplifiers and/or frequency multipliers.

If, for some reason, grid neutralization of the amplitude modulator tubes G and H of stage C is preferable, the circuit arrangement of Figure 5 may be used. Y

In Figure 5 the source of oscillations A is coupled by way of blocking condensers I and 3' to points Von the inductance 4! of the grid tank circuit X. This tank circuit X is tuned to the de-V sired frequency by variable capacity 4I, and the natural impedance of this tuned circuit X to the oscillations from A is such as to match the low impedance output of A to the high impedance of the input electrodes of tubes G and H. The high frequency oscillations from tank circuit X are applied in phase opposition to the control electrodes 2 and 4 of tubes G and H. The high frequency oscillations repeated or multiplied in tubes G and H are fed to tank circuits M and N, as in the prior arrangement. However, in this ,arrangement, since the high frequency oscillations are applied in phase opposition to the control electrodes and not cophasally, as in the prior arrangement, reversal of the energy in one of the amplitude modulators G and H must be accomplished in order to properly combine the energies lead through the phase shifting means L and Q to the grid electrode S of tube V. This is accomplished by reversing the coupling of one of the tank circuits M and N with its tube G or H. In Figure 5 the coupling between the Vtank circuit N and tube H is reversed. In other words, the output circuits of these tubes are, in a manner, connected in push-pull so that the energies therein are alike in phase. The phase shifting circuits L and Q are tapped to points on the inductances I I and II such that the energy drawn from the tank circuits M and N is in phase and is fed to the control grid S in phase except for the phase shift accomplished by the phase shifting elements L and Q. In this arrangement the grid'to anode capacity of the tubes G and-H is neutralized or mental or to a harmonic. 'suggested that a slight amount of mutual induc- .compensated by connecting the anode 6 of tube G to the control electrode 4 of tube H and the anode 8 of tube H tothe control electrode 2 of tube G by way of neutralizing condensers NC and NC, as

shown. Biasing potential for the control electrodes 2 and 4 of tubes G and H is supplied by way of a lead 34.' connecting a point on potentiometer P1 to the midpoint of inductance 40, which has its terminals conductively connectedv to the control Velectrodes 2 and 4. The arrangement or Figure 5 is otherwise the same as the arrangement of Figure 4.

It will be noted, however, that in Figures 4 and 5 the inductance I4 of stage D has been replaced by a resistance I 4I. It will be understood that either aninductance or a resistance may be used, but it is preferable to use resistance, at this point.

In operation the arrangement of Figure 5 operates substantially the same as the arrangement of Figure 4; However, since there has been a shift in phase of the high frequency oscillations applied to the control electrode 4 with'respect to the phase of the high frequency oscillations applied to the same control electrode in Figure 4, there must be a second reversal in phase of the energy accomplished before the energy is applied to the phase shifting elements L and Q and from said'elements to the control grid S of modulator tube V. This is accomplished, as indicated above, by reversing the connectionbetween the anode electrode 8 of tube H and the tank circuit N, as shown. This brings amplified and amplitude modulated energies in the tank circuit in phase. The amplified and amplitude modulated and/or frequency multiplied energies in the tank circuits M and Nare fed by way of phase shifting elements L and Q to the modulator tube, as in the prior arrangements. This modulation is accomplished in the tube V in the arrangement of Figure 5 and the phase modulated and amplitude modulated energyrin the tank circuit R is fed by way of unit E, which may include all of the elements included in the like unitV in the prior iigures, to the load circuit F.

In the operation of thearrangements shown in Figures 1 to 5 inclusive the tank circuits M and N should be tuned alike, that is, to the same frequency, whether they are tuned to a funda- In some cases it is tive coupling between the two circuits M and N be maintained in the proper direction to aid in keeping the two modulator tubes G and H in step. In some cases this should improve the operation of the transmitter. Moreover, it will be understood that thephase shifting elements L and Q may take the form of inductances and capacities, or any combination thereof, or may be replaced by transmission lines of the proper length. These lines may be artificial lines and may include tuning means. All that is necessary is that the desired amount of phase shift is introduced into the amplitude modulator carrier energy reaching the tubeV.

Moreover, it will be understood that tubes of anytype known may be used to replace the tubes used in the circuits included above, which are intended to be illustrative of the invention and are not intended to limit the invention in any manner except as limited in the claims appended hereto.

When the tubes G and H are used as frequency multipliers as well as Vamplitude modulators, feed back coupling in these circuits may be resorted to to enhance the frequency multiplying effect. This 75 may be accomplished in the'arrangmnts illustrated in Figures 4 and 5 by over-neutralizing the circuits by means of the neutralizing condensers NC and NC'. That is, the coupling between the input and output circuits of tubes G and H may be increased byy these condenserssufciently to insure the desired amount of regeneration.

Having thus described my invention andthe operation thereof, whatI claim is:

1. Transmitting means comprising, a source of oscillations, a pair of thermionic tubes, means for connecting said source of oscillations in phase to the control electrodes of said tubes, a separate tank circuit connected to the anode of each of said tubes, a source of modulating frequencies, means for impressing the modulating frequencies in phase opposition on the output electrodes of said tubes, a modulator tube, and separate phase shifting means connecting the control electrode of said modulator tube to each tank circuit.

2. Means for relaying vand phase modulating high frequency energy comprising, a pair of thermionic tubes having their input electrodes energized in phase by a carrier frequency wavea thermionic modulator tube, phase retarding means for applying energy from the anode of one of said tubes to the control electrode of said modulator tube, phase advancing means for applying energy fro-1n the anode of the other of said tubes to the same control electrode of said modulator tube, and means for impressing in phase opposition modulating potentials on the anode electrodes of said pair of tubes.

3. Transmitting means comprising, a source'of oscillations, a pair of thermionic tubes, a circuit connecting said source of loscillations to the control electrodes of said tubes to apply thereto oscillations of like phase, a separate tank circuit connected to the anode of each of said tubes, there being appreciable coupling between said tank circuits, means for tuning said tank circuits to a frequency which is a harmonic of the frequency of said source, a source of modulating frequencies, means for impressing the modulating frequencies in phase opposition on the anode electrodes of said tubes, a modulator tube, and separate phase shifting means connecting the control electrode of said modulator tube to each tank circuit.

4. Signalling means comprising, a pair of thermionic tubes, an input circuit including similar reactances connecting the control electrodes of said tubes together, a separate output circuit connected with the anodes of each of said tubes, symmetrical neutralization circuits connected between the anodes and control electrodes of each of said tubes, means in each of said output circuits for tuning said output circuits to a frequency which is a multiple of the frequency of said input circuit, means for applying high frequency oscillations in phase to the similar reactances in said inputcircuit, means for varying the impedance of said tubes oppo-sitely at signal frequency, a thermionic phase modulator, and impedances connecting each of said tank circuits to an electrode in said modulator tube.

5. Signalling means comprising, a source of constant frequency oscillations, a thermionic modulator tube, a pair of thermionic frequency multipliers and ampliers having an input circuit and separate anode circuits, a circuit for applying energy of like phase from said source of constant frequency oscillations to the input circuits of said pair of tubes, regenerative coupling between the input circuits and output circuits of said amplifiers and frequency multipliers, means for applying signal potentials in phase opposition to the anode electrodes of said frequency multipliers and amplifiers, phase shifting means of different characteristic connecting each of said anode circuits to the control electrode of said modulator tube, and a resistance connected between the control electrode and cathode of said modulator tube.

6. In a phase modulation system, a pair of thermionictubes each having an input electrode energized in phase by a carrier frequencywave, said tubes each having an output circuit, means for tuning said output circuits to a harmonic of the frequency at which the input electrodes are' energized, means for producing regeneration in each of said tubes comprising a capacity connecting anY output eiectro-de to an input electrode, a circuitk for varying the internal impedance of each of said tubes in phase opposition at signal frequency, a utilization circuit, and phase shifting reactances of different character connecting said output circuits to said utilization circuit. f

7. Phase modulating means comprising, a pair of thermionic amplifiers and frequency multipliers of the triode type, a common input circuit connected with the input electrodes of said amplifiers and frequency multipliers, means for energizing said input circuit by waves of carrier frequency, an output circuit connected to each amplifier and frequency multiplier, means for tuning the output circuits of each of said amplifiers and frequency multipliers to a harmonic of the energizing frequency, means for insuring controlled regeneration in each of said tubes including a variable capacity connecting a point on the output circuit of each of said tubes to the input electrode of said tube, means forV varying the internal impedance of said tubes in phase opposition at signal frequency, a thermionic modulator tube having a resistance connected between its input electrodes, and phase shifting means for connecting said input electrodes to each of said output circuits.

8. Means for relaying and phase modulating carrier frequency energy comprising, a pair of thermionic tubes having their input electrodes energized in phase by a carrier frequency wave, a thermionic modulator tube, a phase advancing reactance for applying energy from the anode of one of said pair of tubes to a control electrode in said modulator, a phase retarding reactance for applying energy from the anode of the other of said pair of tubes to a control electrode in said modulator, and circuits connected with the anode of each of said pair of tubes for impressing modulating potentials on the internal impedances of said tubes.

9. Phase modulating means comprising, a pair of thermionic tubes each having an anode and a control grid, a source of oscillations, circuits for applying oscillations from said source in phase to the control electrodes of said tubes, tank circuits connected with the anodes of each of said tubes, said tank circuits being connected in parallel relation, a modulator tube, a reactance connecting one of said tank circuits toa control electrode in said modulator tube, a second reactance of different character connecting the other of said tank circuits to the control electrode in said modulator' tube, and circuits connected with the anode of each tube of said pair of tubes on the one hand and with a source of modulating potential on the other hand.

10. Transmitting means comprising, a source of oscillations, a pair of thermionic tubes, similar separate reactances connecting said source of oscillations to the control electrodes of said tubes to apply to said control electrodes oscillations of like phase, a separate tank circuit connected to the anode of each of said tubes, means for tuning each of' said tank circuits, a source of modulating potentials, circuits connecting said source of modulating potentials in phase opposition to the anode electrodes of said pair of tubes, a modulator tube, separate dissimilar reactances connecting the control electrode of said modulator tube to each tank circuit, and an impedance connected between the control electrode and cathode of said modulator tube.

11. Transmitting means comprising, a source of oscillations, a pair of thermionic tubes, similar reactances connecting said source of oscillations to the control electrodes of said tubes to apply to said -control electrodes oscillations of like phase, a separate tank circuit connected to the anode of each of said tubes, means for tuning each of said tank circuits, a source of modulating potentials, circuits connecting said source of modulating potentials in phase opposition to the anodes ofsaid tubes, a modulator tube, separate dissimi-v lar reactances connecting the control electrode of said modulator tube to each tank circuit, a resistance connected between the control electrodes and cathode of said modulator tube and circuits connected with the anodes and control electrodes of each tube of said pair of tubes for neutralizing the eiect of the inherent capacity between said electrodes within the tube.

12. In a signalling system, a pair of thermionic `tubes each having an anodeiand a control grid,'a

common input circuit connected to the control grids of said tubes, a pair of similar reactances in series in said input circuit, neutralizing circults connected to the anodes and control grids of said tubes, a separate output circuit connected with the anode of each of said tubes, a circuit connected Vto a point between said similar reactances for applying carrier Waves to be modulated on said input circuit, circuits connected with the anodes of said tubes for varying the impedances of said tubesV in phase opposition at signal frequency, a common utilization circuit, and separate phase shifting reactances of different character connecting said output circuits to said common utilization circuit. Y

13. Modulating means comprising, a pair of thermionic tubes each having an anode, a cathode and a control grid, a source of carrier frequency oscillations, circuits connecting the controlgrid of each of said tubes to said source of carrier frequency oscillations, a tuned tankV circuit connected between the anode and cathode of each of said tubes, neutralizing condensers connected with each of said tubes for neutralizing the inherent capacity between the control grid and anode o-f each of said tubes, a modulator tube, an inductive reactance connecting one of said tank circuits to the control grid of said modulator tube, a capacitive reactance connecting the other of said tank circuits to the control grid of said modulator tube, an impedance connected betweenV the control grid and cathode of said modulator tube, a utilization circuit connected between the anode and cathode of said modulator tube, a source of modulating potentials,

a transformer having itsY primary winding connected to said source, and circuits connecting the secondary winding of said transformer to the anodes of said pair of tubes.

GEORGE LINDLEY USSELMAN. 

